Area Forecast Discussion
Issued by NWS Goodland, KS
Issued by NWS Goodland, KS
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214 FXUS63 KGLD 210925 AFDGLD Area Forecast Discussion National Weather Service Goodland KS 325 AM MDT Sat Sep 21 2024 .KEY MESSAGES... - Showers and thunderstorms will develop over majority of the Tri-State area this weekend. Both severe weather and flooding chances are very low (<5%). - Low temperatures in the mid to upper 30s are forecast for eastern Colorado by Monday morning. There is a concern for fog formation Monday morning, too. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 320 AM MDT Sat Sep 21 2024 This morning, the low pressure system that we have been monitoring for the past week will be near the Four Corners region and moving east-northeast. Over the past few days, guidance has been very gradually slowing this low, which is delaying the start of the precipitation. Another notable change over the previous 36-48 hours is that the low looks to be taking a more easterly path than previously thought. These two changes have broadened out the low, making it weaker, and has shifted it`s main path farther south, likely over the south-central CWA when it finally crosses. The broadening will push a the cold front into the area early this morning, likely crossing the entire CWA by 18Z. With this cold front, northerly winds sustained around 20-25 kts and gusts around 35 kts are expected this morning and mid-day. These winds will cause temperatures to remain cool, likely hitting maximum temperatures before noon. Temperatures today in the northwestern CWA will be in the low 70s, but the southeastern CWA will still warm into the low 80s before the cold front passes. This cold front coming earlier than previously thought, and the more southern track, has lowered total QPF for the northwestern half of the CWA. Guidance is showing the 500mb shortwave that will set off the precipitation will start forming showers and storms south of the CWA by 16-18Z. Over the following hours, this precipitation will move northeastward while new showers will form west of the already existing precipitation. No later than 21Z, we expect to see precipitation in the CWA. The best coverage of rain for will start around 0Z. From 0Z through 12Z, all of the CWA will have 50-75+ PoPs. After 12Z, PoPs taper off from the southwest as drier air moves in and pressure rises occur following the low. By 0Z Monday, all of the precipitation will have moved out of the area. For more information about the precipitation, see the hydrology discussion below. Severe convective weather seems extremely unlikely (<2% chance) due to a lack of instability. Temperatures overnight tonight will be a balancing act between the CAA and the clouds insulating us. Currently we expect lows to cool into the mid 40s in the west to low 50s in the east. However, if the northerly winds are stronger, expect cooler temperatures (~5 degrees cooler), but if the winds/CAA weaken, expect lows near 50 for the entire Tri-State area. Sunday`s high temperatures will be the coolest we`ve seen so far this season. The clouds and northerly winds will prevent majority of the day time heating. Temperatures are expected to remain in the low to mid 50s Sunday. As the low moves out of the area Sunday afternoon/evening, winds will weaken and the sky will clear out. This is creating an interesting setup overnight Sunday where two things could happen, or a mixture of both. Potential one is patchy to widespread fog; with clear skies, light winds, and recent precipitation, the environment is primed for fog formation, with a catch. The light winds that will exist will be westerly, downslope winds, which will work to prevent fog formation. Most likely scenario is valleys and locations sheltered from the light breezes will see fog form, but if the winds drop to 0, widespread fog could easily form. Potential two is frost formation, mainly in eastern Colorado. The same conditions that make fog possible/likely Sunday (minus the moisture) could allow for temperatures to drop into the mid 30s, allowing for light, patchy frost to form. The big unknown, and biggest limiting factor, for the frost potential is what the dew points will do Sunday evening/overnight. If dew points remain in the low 40s in eastern Colorado Sunday evening/night, the potential for frost is near 0. However, if the dew points are in the mid 30s, patchy frost becomes more likely. Confidence for "potential one," the fog, occurring is around 30% and could impact majority of the CWA. Confidence for "potential two," the frost, occurring is around 25%, but looks to be limited to our Colorado counties. As mentioned before, there is a chance (~20%) that both could occur; we could see fog in the eastern CWA and frost in the western CWA. We will be monitoring this closely over the next 36 hour. && .LONG TERM /MONDAY THROUGH FRIDAY/... Issued at 245 AM MDT Sat Sep 21 2024 Monday: Guidance suggests that troughing/cyclonic flow aloft will persist over the Central Plains.. on the eastern fringe of an amplifying upper level ridge along the Pacific Coast. Clear skies in the wake of the departing wave may eventually give way to increasing cloud cover late Mon-Mon night.. via cyclonic shear vorticity on the eastern periphery of a strong (~100-115 knot) northerly upper level jet extending southward from Alberta and Saskatchewan to the central Rockies. Sunny skies during the day will foster a warming trend. Expect temperatures warmer than Sunday (albeit still cooler than average).. ranging from the mid 60s (east) to mid 70s (west). Tuesday-Friday: Below average forecast confidence. Forecast confidence typically decreases with range -- `below average` in this context is intended to communicate a further reduction in confidence associated with /inherent to/ increased pattern complexity -- e.g. patterns with cut-off waves, multibranched wave interactions and potentially significant forms of constructive/destructive interference or feedback. Solutions from current operational runs of the GFS/ECMWF continue to diverge on Tuesday.. albeit less-so than yesterday. Both models suggest that [1] the aforementioned ridge will shift eastward across the Intermountain West (Tue), Rockies (Wed), Central/Northern Plains (Thu) and Mississippi River Valley (Fri).. [2] that some degree of northern and southern stream jet phasing (or interaction) within a complex split flow regime on the eastern periphery of the advancing ridge will foster the development of a closed low and [3] that said low will be subsumed by /trapped within, cut-off beneath/ the ridge. The ECMWF suggests that upper low development and subsumption will occur over the Central-Southern Plains.. the GFS suggests it will occur over the OH Valley. Steering the forecast toward climatology appears to be the most prudent course of action at this time. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1036 PM MDT Fri Sep 20 2024 VFR expected to prevail at both KGLD and KMCK through the TAF period. A cold front will shift winds to the northwest then northeast early Saturday morning, gusty through the afternoon. Some showers may begin to move into the area towards the end of the TAF period Saturday night, but with minimal, if any, impacts. && .HYDROLOGY... Issued at 320 AM MDT Sat Sep 21 2024 The 850mb LLJ has been moving moisture into the Great Plains overnight and will continue into Sunday, following the low as it moves east out of the area. Due to the more southerly path the low is expected to take and the early cold front, most of this moisture will not directly be moved into the CWA. The moisture will instead be moved into the area by the low as wrap-around moisture, as seen on 315K maps. Precipitation looks to start in the eastern CWA late Saturday morning/early afternoon, intensifying Saturday evening, and begin weakening Sunday morning/mid-day before moving out of the area by Sunday evening. Between 0Z-12Z Sunday, nearly the entire Tri-State area will see at least a few tenths of rain with the potential (20- 25%) of seeing 1+ inches in that timeframe. Concerns for flash flooding are low (<5%) with the potential for areal or river flooding being slightly higher at around 20%. Throughout the entire event, locations along and southeast of a line from Wallace, KS to Hill City, KS can expect to see .9-1.7 inches of rain, with pockets of 2.5+ inches being possible. Locations west and north of that line, but south of HWY 36 will receive around 0.4-1 inch of rain, with some pockets up to 1.75 inches. Areas north of HWY 36 will see the least amount of rain, generally ranging from around 0.25-.8 inches. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...None. CO...None. NE...None. && $$ SHORT TERM...CA LONG TERM...Vincent AVIATION...024 HYDROLOGY...CA